Hydrogen sulfide is a flammable, toxic gas, which is formed by subjecting sulfur compounds contained in oil or natural gas to hydrodesulfurization, and is recovered as solid sulfur by means of a sulfur recovery unit. Hydrogen sulfide is also a valuable compound as a starting material for synthesis of various sulfur-containing compounds. Hydrogen sulfide or sodium hydrogen sulfide formed from hydrogen sulfide and sodium hydroxide has been widely used as a starting material for preparing fine chemicals, such as dyes, agrochemicals, plastics, drugs, and cosmetics, and as a starting material for producing metal sulfides.
As a method for producing hydrogen sulfide from sulfur and hydrogen using a gas-phase reaction, the following two methods are known.
(1) Catalyzed Reaction
In a reaction tube filled with a catalyst, sulfur gas and hydrogen gas react with each other to form hydrogen sulfide. The reaction heat is removed by circulating a heating medium outside the reaction tube. Such a catalyzed reaction is, for example, disclosed in Patent Literature 1 described below.
(2) Uncatalyzed Reaction
An uncatalyzed gas-phase reaction is, for example, illustrated in FIG. 1 on page 474 of Non Patent Literature 1 described below. In the uncatalyzed gas-phase reaction, hydrogen sulfide is produced using a reactor column having a bottom portion that retains liquid sulfur at the boiling temperature thereof and a gas space in which sulfur gas and hydrogen gas are reacted with each other. Hydrogen gas is introduced into liquid sulfur in the bottom portion, and hydrogen gas and sulfur gas react with each other in the gas space to form hydrogen sulfide. The reaction heat of hydrogen sulfide is recovered by being brought into contact with liquid sulfur which is supplied from the upper part of the gas space. The product gas containing hydrogen sulfide and sulfur gas is cooled by a heat exchanger to solidify sulfur, thereby purifying hydrogen sulfide gas.    PTL 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-515658    NPL 1: Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, 1996, Vol. A13, pp. 467˜485.